<!DOCTYPE html>
<html>
	<head>
		<title>文档的标题</title>
		<style>
			a {
				margin: 100px;
			}
			a.tooltip {
				border-bottom: 1px dashed;
				text-decoration: none;
			}
			a.tooltip:hover {
				cursor: help;
				position: relative;
			}
			a.tooltip span {
				display: none;
			}
			a.tooltip:hover span {
				border: #666 1px solid;
				padding: 5px 20px;
				display: block;
				z-index: 100;
				background: #e3e3e3;
				left: 0px;
				margin: 15px;
				width: 300px;
				position: absolute;
				top: 15px;
				text-decoration: none;
			}
		</style>
	</head>
	<body>
		<a href="#" class="tooltip">
            Mouse over the link
			<span>当鼠标悬停在链接上时显示 CSS 工具提示</span>
		</a>
	</body>
</html>
